Network Address Translation Questions and Answers

Q: Which command will clear all the translations active on your router?

Correct answer: clear ip nat translations *The asterisk clears every dynamic entry in the table, which is the usual way of forcing translations to be rebuilt after a configuration change - a stale entry will otherwise persist until its timeout. A specific entry can be cleared by giving its addresses instead, and static translations are removed by deleting their configuration rather than by this command.

Q: When creating a pool of global addresses, which of the following can be used instead of the netmask command?

Correct answer: prefix-lengthThe pool can be defined either as netmask 255.255.255.0 or as prefix-length 24 - the two are equivalent and one or the other must appear. Slash notation is not accepted in this command, and block-size belongs to wireless configuration rather than to NAT.

Q: Which command will show you the summary of the NAT configuration?

The show ip nat statistics command displays a summary of the NAT configuration as well as counts of active translation types, hits to an existing mapping, misses (causing an attempt to create a mapping), and expired translations.

Q: Which command will allow you to see real-time translations on your router?

Correct answer: debug ip natdebug ip nat prints each translation as it is created and used, so it shows the process happening rather than the table that resulted. That makes it the tool when the question is why a particular flow is not being translated - and, as always with debug on a busy router, it should be enabled briefly and with the output directed somewhere it can be read.

Q: Which command will create a dynamic pool named Todd that will provide you with 30 global addresses?

The command ip nat pool creates the pool that hosts can use to get onto the global Internet. What makes option B correct is that the range 171.16.10.65 through 171.16.10.94 includes 30 hosts, but the mask has to match 30 hosts as well, and that mask is 255.255.255.224. Option C is wrong because the pool name has a lower case "T" in the pool name. Pool name's are case sensitive.

Q: Port Address Translation is also termed what?

Correct answer: NAT OverloadPort Address Translation and NAT Overload are the same thing under two names: many inside hosts share one global address, distinguished by the source port the router assigns to each session. It is what allows an entire site to sit behind a single public address, and it is by far the most common form of NAT in use.

Q: Which of the following would be good reasons to run NAT? 1.You need to connect to the Internet and your hosts don't have globally unique IP addresses. 2.You change to a new ISP that requires you to renumber your network. 3.You don't want any hosts connecting to the Internet. 4.You require two intranets with duplicate addresses to merge.

Correct answer: 1, 2 and 4All three are standard reasons: private addressing behind a public one, renumbering avoided when changing ISP by translating at the boundary, and merging two intranets whose address ranges overlap. Statement 3 is not a NAT use - if no host is to reach the internet, the answer is not to route or to filter, not to translate.

Q: Which of the following are disadvantages of using NAT? 1.Translation introduces switching path delays. 2.Conserves legally registered addresses. 3.Causes loss of end-to-end IP traceability. 4.Increases flexibility when connecting to the Internet. 5.Certain applications will not function with NAT enabled. 6.Reduces address overlap occurrence.

Correct answer: 1, 3 and 5The genuine disadvantages are the switching delay translation adds, the loss of end-to-end traceability since the original source is hidden, and the applications that break because they carry addresses inside the payload - older FTP, SIP and IPSec among them. Statements 2, 4 and 6 are advantages of NAT rather than drawbacks, and are there to be sorted out.

11.

Which command will clear all the translations active on your router?

A.show ip nat translations
B.show ip nat statistics
C.debug ip nat
D.clear ip nat translations *

Answer: D

Correct answer: clear ip nat translations *

The asterisk clears every dynamic entry in the table, which is the usual way of forcing translations to be rebuilt after a configuration change - a stale entry will otherwise persist until its timeout. A specific entry can be cleared by giving its addresses instead, and static translations are removed by deleting their configuration rather than by this command.

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12.

When creating a pool of global addresses, which of the following can be used instead of the netmask command?

A./ (slash notation)
B.prefix-length
C.no mask
D.block-size

Answer: B

Correct answer: prefix-length

The pool can be defined either as netmask 255.255.255.0 or as prefix-length 24 - the two are equivalent and one or the other must appear. Slash notation is not accepted in this command, and block-size belongs to wireless configuration rather than to NAT.

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13.

Which command will show you the summary of the NAT configuration?

A.show ip nat translations
B.show ip nat statistics
C.debug ip nat
D.clear ip nat translations *

Answer: B

The show ip nat statistics command displays a summary of the NAT configuration as well as counts of active translation types, hits to an existing mapping, misses (causing an attempt to create a mapping), and expired translations.

Discuss in Forum

14.

Which command will allow you to see real-time translations on your router?

A.show ip nat translations
B.show ip nat statistics
C.debug ip nat
D.clear ip nat translations *

Answer: C

Correct answer: debug ip nat

debug ip nat prints each translation as it is created and used, so it shows the process happening rather than the table that resulted. That makes it the tool when the question is why a particular flow is not being translated - and, as always with debug on a busy router, it should be enabled briefly and with the output directed somewhere it can be read.

Discuss in Forum

15.

Which command would you place on interface on a private network?

A.ip nat inside
B.ip nat outside
C.ip outside global
D.ip inside local

Answer: A

As in access-lists, you must configure your interfaces before NAT will provide any translations. On the inside networks you would use the command ip nat inside. On the outside interface, you will use the command ip nat outside.

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16.

Which command will create a dynamic pool named Todd that will provide you with 30 global addresses?

A.ip nat pool Todd 171.16.10.65 171.16.10.94 net 255.255.255.240
B.ip nat pool Todd 171.16.10.65 171.16.10.94 net 255.255.255.224
C.ip nat pool todd 171.16.10.65 171.16.10.94 net 255.255.255.224
D.ip nat pool Todd 171.16.10.1 171.16.10.254 net 255.255.255.0

Answer: B

The command ip nat pool creates the pool that hosts can use to get onto the global Internet. What makes option B correct is that the range 171.16.10.65 through 171.16.10.94 includes 30 hosts, but the mask has to match 30 hosts as well, and that mask is 255.255.255.224. Option C is wrong because the pool name has a lower case "T" in the pool name. Pool name's are case sensitive.

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17.

Port Address Translation is also termed what?

A.NAT Fast
B.NAT Static
C.NAT Overload
D.Overloading Static

Answer: C

Correct answer: NAT Overload

Port Address Translation and NAT Overload are the same thing under two names: many inside hosts share one global address, distinguished by the source port the router assigns to each session. It is what allows an entire site to sit behind a single public address, and it is by far the most common form of NAT in use.

Discuss in Forum

18.

Which of the following would be good reasons to run NAT?

1.You need to connect to the Internet and your hosts don't have globally unique IP addresses.

2.You change to a new ISP that requires you to renumber your network.

3.You don't want any hosts connecting to the Internet.

4.You require two intranets with duplicate addresses to merge.

A.1, 2 and 4
B.2 and 4
C.3 only
D.All of the above

Answer: A

Correct answer: 1, 2 and 4

All three are standard reasons: private addressing behind a public one, renumbering avoided when changing ISP by translating at the boundary, and merging two intranets whose address ranges overlap. Statement 3 is not a NAT use - if no host is to reach the internet, the answer is not to route or to filter, not to translate.

Discuss in Forum

19.

Which of the following are disadvantages of using NAT?

1.Translation introduces switching path delays.

2.Conserves legally registered addresses.

3.Causes loss of end-to-end IP traceability.

4.Increases flexibility when connecting to the Internet.

5.Certain applications will not function with NAT enabled.

6.Reduces address overlap occurrence.

A.1, 3 and 5
B.3 and 4
C.2, 4 and 5
D.1 and 3

Answer: A

Correct answer: 1, 3 and 5

The genuine disadvantages are the switching delay translation adds, the loss of end-to-end traceability since the original source is hidden, and the applications that break because they carry addresses inside the payload - older FTP, SIP and IPSec among them. Statements 2, 4 and 6 are advantages of NAT rather than drawbacks, and are there to be sorted out.

Discuss in Forum

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Network Address Translation Questions and Answers

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